Prosthetic valves have proven to be a most beneficial treatment option in replacing diseased or malfunctioning native valves. Over the years, prosthetic heart valves have saved hundreds of thousands of lives. Prosthetic venous valves promise a treatment option for a large group of patients suffering from the consequences of lost or damaged valves, for example, in their deep veins.
Native valves have leaflets that act as one-way check valve and open to permit fluid flow through vessels in the forward or antegrade direction and close to substantially prevent fluid flow in a reverse or retrograde direction. Leaflets can change from an open position in response to a variety of circumstances, including changes in the cross-sectional shape of the vessel, and the fluid pressure within the vessel.
Unfortunately, native valves may lose their effectiveness leading to potentially life threatening conditions. For example, over time, the vessel wall may stretch, or the leaflet may become damaged due to disease or occlusion affecting the valve leaflet's ability to close resulting in changes in fluid flow, which may lead to, in severe cases, the insufficiency of the venous system of a limb and the pain, swelling, ulcers, thrombosis, a loss of quality of life, disability and even death.
In the past, conventional prosthetic valves have been designed to mimic native valving function as soon as they are implanted. That is, immediately after the valve is implanted in the body, the leaflets open at a certain fluid pressure and close at a certain pressure to prevent fluid flow in the retrograde direction. Indeed, most prior art valves have been designed to prevent fluid flow in the retrograde direction. A conventional prosthetic valve that stayed restrained in one position regardless of the fluid pressure would be considered defective and, if implanted in the body, may need to be removed.
By designing prosthetic valves to start their valving function immediately after they are implanted, gross fluid flow changes are promoted contributing to the formation of abnormal (e.g. turbulent) flow and thrombi (blood clots) at or around the site of implantation. Other factors that may lead to thrombosis include excessive trauma to the vessel's intima during implantation and the particular materials used to make the valve that may be thrombogenic. These factors (e.g., gross flow changes that may include thrombogenic turbulent flow, thrombogenicity of the valve, and trauma to the implantation site) all reduce prosthetic valve survival. Indeed, today there is no commonly accepted and widely used prosthetic venous valve available to the practicing physician, as most valve designs fail after implantation, primarily due to thrombosis (blood clot formation).
Minimally invasive percutaneous, and interventional techniques used to place the prosthetic valve at the implant site, sophisticated interventional devices such as catheters and delivery systems, as well as medical therapies applied in conjunction with the interventional approach, have been developed to reduce trauma to the vessel and in turn reduce the risk of thrombosis and thus increase prosthetic valve survival.
New implantable prosthetic valves and methods are still needed that delay gross flow changes and the development of abnormal, thrombogenic flow patterns that immediately follow the implantation of prosthetic valves of conventional designs.